Such a brake system is disclosed, for example, by the international patent application WO 01/72567 A1. A perceived disadvantage of the known brake system is the energy efficiency of the known brake system, two aspects of which seem open to improvement.
In the preferred “brake-by-wire” operating mode, even slight braking, which does not involve great dynamics or require individual wheel brake pressure adjustment, is achieved by a hydraulic fluid volume drawn from the high-pressure accumulator. Thereafter the accumulator has to be recharged with an input of energy significantly greater than the hydraulic energy used. This applies to the majority of braking actions that occur in average driving. From the point of view of energy consumption it is therefore advisable to use hydraulic fluid from the hydraulic accumulator only when dynamic braking is required, and preferably to perform braking actions directly by means of the pressure of the electrically controllable pressure source.
In a fall-back operating mode, in which electrical control is unavailable but hydraulic power is available in the form of pressure and hydraulic fluid volume in the hydraulic accumulator, the known brake system (as in the “brake-by-wire” operating mode) functions as power brake system. It seems more sensible here not to dispense with the actuating energy contributed by the vehicle driver actuating the brake pedal, but to utilize this. It therefore makes more sense in this operating situation for the new brake system proposed here to function as power-assisted brake system.
The present invention creates the technical prerequisites for improving the energy efficiency on both counts.